Pretty much any of the Shin Meguni Tensei/Persona games. I love those games, but tend to get bored around the 60 hour mark due to all the grinding and monster collecting. To this day, I haven't beaten any of them, but it is one of my favorite series.
Oblivion, I find the hell gates to be so boring. I love questing, not going into what amounts to a Doom area of the game with my stealth character.
Rule of Rose, it is a survival horror with of an orphanage mixed with Lord of the Flies. The story is amazing, but the battle system is so broken. Your weapon goes through bad guys at times, it is easy to get knocked down and can't do anything, the bosses are incredibly cheap. I got really far just.... ugh.